The present invention relates to a locking nail to treat fractures of tubular bones. The invention also relates to an aiming or targeting apparatus for a locking nail.
Locking nails for treating fractures of, for example, a femur, humerus and tibia, are known. It is common for locking nails to have cross-bores at the distal end and at least one cross-bore at the proximal end. Typically, bone screws are passed through the cross-bores which screws have been screwed into the corticalis at the opposite side of the bone. The bone screws secure the locking nail axially and rotationally. If supracondylar nails are used condylus screws may also be passed through the cross-bores.
A problem in employing locking nails, when inserted, is how to identify the position of the cross-bores to drill a hole into the corticalis in the proper place from outside. A number of aiming or targeting apparatus have become known, which work with X-rays to identify the position of the cross-bore relative to the targeting apparatus. Therefore, it is possible to drill a hole into the bone in the proper place by use of the targeting apparatus and a so-called drilling sleeve or aiming sleeve. In most cases, known targeting apparatus are firmly connected to the end of the nail used to drive in the nail. Thus, the position of the cross-bores may already be preset in an approximately precise way. However, it should be considered that the presumed position of the cross-bores will not coincide with the real one because of the curvature of the bone and the possible torsion the nail undergoes while it is driven in.
The disadvantage of using the targeting apparatus working with X-rays is that both the operator and patient are exposed to a radiation dose. Therefore, targeting apparatus are known that do not use radiography, but allow for the identification of the location of the cross-bore mechanically. Such are shown in U.S. Pat. Nos. 5,176,681, 5,334,192 and 6,039,739. Since it is necessary for the targeting apparatus to be connected to the locking nail it has hitherto been impossible to identify the location of cross-bores and to introduce bone screws for those positioned close to the nail end. This is why cross-bores always need to be at a minimum distance from the end of the locking nail.